package com.starnet.utils;
import java.io.ByteArrayOutputStream;  
import java.io.IOException;  
import java.io.OutputStream;  
  
/** 
 * Base64编码工具类 
 */  
public class Base64 {  
  private static final char[] legalChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/".toCharArray();  
 
   public static String encode(byte[] data) {  
       int start = 0;  
       int len = data.length;  
       StringBuffer buf = new StringBuffer(data.length * 3 / 2);  
 
       int end = len - 3;  
       int i = start;  
       int n = 0;  
 
       while (i <= end) {  
           int d = ((((int) data[i]) & 0x0ff) << 16) | ((((int) data[i + 1]) & 0x0ff) << 8) | (((int) data[i + 2]) & 0x0ff);  
 
           buf.append(legalChars[(d >> 18) & 63]);  
           buf.append(legalChars[(d >> 12) & 63]);  
           buf.append(legalChars[(d >> 6) & 63]);  
           buf.append(legalChars[d & 63]);  
 
           i += 3;  
 
           if (n++ >= 14) {  
               n = 0;  
               buf.append(" ");  
           }  
       }  
 
       if (i == start + len - 2) {  
           int d = ((((int) data[i]) & 0x0ff) << 16) | ((((int) data[i + 1]) & 255) << 8);  
 
           buf.append(legalChars[(d >> 18) & 63]);  
           buf.append(legalChars[(d >> 12) & 63]);  
           buf.append(legalChars[(d >> 6) & 63]);  
           buf.append("=");  
       } else if (i == start + len - 1) {  
           int d = (((int) data[i]) & 0x0ff) << 16;  
 
           buf.append(legalChars[(d >> 18) & 63]);  
           buf.append(legalChars[(d >> 12) & 63]);  
           buf.append("==");  
       }  
 
       return buf.toString();  
   }  
 
   private static int decode(char c) {  
       if (c >= 'A' && c <= 'Z')  
           return ((int) c) - 65;  
       else if (c >= 'a' && c <= 'z')  
           return ((int) c) - 97 + 26;  
       else if (c >= '0' && c <= '9')  
           return ((int) c) - 48 + 26 + 26;  
       else  
           switch (c) {  
           case '+':  
               return 62;  
           case '/':  
               return 63;  
           case '=':  
               return 0;  
           default:  
               throw new RuntimeException("unexpected code: " + c);  
           }  
   }  
 
   /** 
    * Decodes the given Base64 encoded String to a new byte array. The byte array holding the decoded data is returned. 
    */  
 
   public static byte[] decode(String s) {  
 
       ByteArrayOutputStream bos = new ByteArrayOutputStream();  
       try {  
           decode(s, bos);  
       } catch (IOException e) {  
           throw new RuntimeException();  
       }  
       byte[] decodedBytes = bos.toByteArray();  
       try {  
           bos.close();  
           bos = null;  
       } catch (IOException ex) {  
           System.err.println("Error while decoding BASE64: " + ex.toString());  
       }  
       return decodedBytes;  
   }  
 
   private static void decode(String s, OutputStream os) throws IOException {  
       int i = 0;  
 
       int len = s.length();  
  
        while (true) {  
            while (i < len && s.charAt(i) <= ' ')  
                i++;  
  
            if (i == len)  
                break;  
  
            int tri = (decode(s.charAt(i)) << 18) + (decode(s.charAt(i + 1)) << 12) + (decode(s.charAt(i + 2)) << 6) + (decode(s.charAt(i + 3)));  
  
            os.write((tri >> 16) & 255);  
            if (s.charAt(i + 2) == '=')  
                break;  
            os.write((tri >> 8) & 255);  
            if (s.charAt(i + 3) == '=')  
                break;  
            os.write(tri & 255);  
  
            i += 4;  
        }  
    }  
}  
